1. Field of the Invention
The present invention relates to a magnetic sensing element in which pinned magnetic layers are disposed at the two sides of the free magnetic layer in the track width direction, in which electric current flows parallel to the surfaces of these layers. In particular, it relates to a magnetic sensing element having improved read outputs and superior sensitivity.
2. Description of the Related Art
A magnetic sensing element constituted from a composite including a free magnetic layer, a nonmagnetic conductive layer, a pinned magnetic layer, and an antiferromagnetic layer stacked in the film thickness direction, in which electric current flows perpendicular to the surface of each layer of the composite, is called current-perpendicular-to-the-plane (CPP) magnetic sensing element. Studies regarding CPP magnetic sensing elements have revealed that the area of the surface of the composite (hereinafter referred to as “element size”) in a plan view must be decreased and the thickness of the composite must be increased in order to yield read outputs sufficient for practical application.
The extent to which the area of the surface of the composite can be decreased is limited according to the current photolithographic technology. Moreover, increasing the thickness of the composite results in an increase in the gap length, which results in degradation of the read characteristics.
Japanese Unexamined Patent Application Publication No. 200-319313, U.S. Pat. No. 6,396,668 B1, and U.S. Pat. No. 6,411,478 B1 disclose magnetic sensing elements in which free magnetic layers, nonmagnetic conductive layers, and pinned magnetic layers are juxtaposed in the track width direction and in which a current is supplied in a direction parallel to the surface of each layer.
The “chip size” and the “thickness” are differently defined between CPP magnetic sensing elements and the magnetic sensing elements described in the aforementioned publications. In the magnetic sensing elements disclosed in the above-described publications, “chip size” as defined in CPP magnetic sensing elements corresponds to the area of a longitudinal cross-section of a magnetic sensing element taken along the thickness direction. Moreover, the “thickness” as defined in CPP magnetic sensing elements corresponds to the length of the magnetic sensing element parallel to the surface of each layer.
Thus, the structure of the magnetic sensing elements disclosed in the above-described publications can easily achieve smaller “chip size” and larger “thickness” as defined in CPP magnetic sensing elements.
However, these publications do not sufficiently provide substantial means for putting these magnetic sensing elements into actual application. First of all, the publications do not identify the structure of a cross-section taken in a direction parallel to each layer of the magnetic sensing element. Since the structure of the cross-section taken parallel to the surface is an important factor for improving the read output, the structure of the cross-section must be investigated in order to put the magnetic sensing element into practical application.
Secondly, structures of the free magnetic layer and the pinned magnetic layer must be investigated in order to improve the read output and the sensitivity since the structures affect bulk scattering.
Thirdly, the means for controlling the magnetization of the free magnetic layer must also be investigated. None of the above-described publications provide sufficient disclosure regarding this point. Controlling the magnetization of the free magnetic layer is an important factor for practical application of the magnetic sensing element.
Japanese Unexamined Patent Application Publication No. 2001-319313 discloses a tunneling magnetoresistive element (TMR element) including a free magnetic layer, a pinned magnetic layer, and a nonmagnetic material layer (barrier layer) between the free magnetic layer and the pinned magnetic layer, in which the nonmagnetic material layer is composed of an insulating material such as Al2O3. In general, TMR elements already have high element resistance; hence, when the structure disclosed in this publication is employed, the resistance will further increase since the area of the cross-section taken in the direction of current flow is decreased, thereby making the practical application more difficult.
In view of the above, the inventors have employed copper to make the nonmagnetic material layer between the free magnetic layer and the pinned magnetic layer so as to make practicable magnetic sensing elements.